Generally, an automobile seat comprises a seat cushion mounted on a floor of an automobile, and a seatback pivotally supported to a rear portion of the seat cushion by recliner devices so as to be pivoted forward and rearward relative to the seat cushion and in such a manner that an angle of the seatback relative to the seat cushion can be adjusted.
The seatback includes a seatback frame which is formed into a substantially quadrilateral shape. The seatback frame comprises a main pipe member of a substantially U-shape arranged with an opening thereof facing downward, an upper frame member formed by press-machining a plate of steel into a predetermined shape and fixed to an upper axial-portion of the main pipe member by welding, left and right side frame members formed by press-machining plates of steel into predetermined shapes and fixed to left and right axial-portions of the main pipe member by welding, and a linear pipe member serving as a lower frame member of the seatback frame, disposed between lower end portions of the left and right axial-portions of the main pipe member and fixed to the lower end portions of the left and right axial-portions of the main pipe member.
There has been known a seatback (Japanese Patent Application Laid-Open No. Hei. 10-103880), in which the linear pipe member of the above-mentioned seatback frame is divided into two pipe member segments in order that impact energy produced by a car crash or the like can be absorbed. Each of the pipe member segments is fixed at an outer end portion thereof to corresponding one of the side frame members by welding. An intermediate pipe member is slidably inserted at both end portions thereof in inner end portions of the pipe member segments.
When the automobile seat is subjected to impact caused by the car crash or the like and a weight load of an occupant on the automobile seat is applied to the seatback, the lower pipe member is operatively made to flex in left, right and rear directions, the pipe member segments are operatively spaced apart from each other in the left and right directions, and the intermediate pipe member is slid relative to the pipe member segments, whereby the entire lower frame member is deformed rearward. Thus, the rearward deformation of the lower frame member is made to thereby absorb the impact.
However, in the automobile seat constructed as discussed above, there is a drawback that, when the weight load of the occupant on the automobile seat is applied to the seatback by the impact, the intermediate pipe member will be unable to be smoothly slid relative to the pipe member segments, thus making it impossible to exhibit a required impact-absorbing function. Moreover, the lower frame member is composed of the pipe member segments and the intermediate pipe member, so that the lower frame member becomes complicated in structure and assembling of the lower frame member is complicated.